While automatic transmissions for wheel loaders change gears in correspondence to vehicle speed, there is an automatic transmission known in the related art that maintains the current gear ratio (hereafter referred to as “speed stage”) in correspondence to the position of a lift arm instead of automatically shifting the speed stage (see patent reference literature 1). This automatic transmission device holds the currently selected speed stage instead of downshifting if the lift arm assumes a position higher than the boom horizontal position.    patent reference literature 1: Japanese Laid Open Patent Publication No. S63-265730